1. Field of the Invention
The invention is based on a fuel injection valve for internal combustion engines.
2. Description of the Invention
One fuel injection valve of the type with which this invention is concerned, is known from German Patent Disclosure DE 19634933A1. In this known valve, on the end toward the combustion chamber of the valve member,there is a valve member tip with two conical faces. A first conical face is adjacent to the valve member shaft and has an opening angel that is less than that of the conical valve seat. The first conical face is adjoined toward the combustion chamber by a second conical face, whose opening angel is greater than that of the valve seat, so that at the transition of the two conical faces, a sealing edge is formed which, in the closing position of the valve member,comes to rest on the valve seat, as a result of a closing force acting on the valve member.
The opening stroke motion of the valve member is exerted by the hydraulic force of the fuel in the pressure chamber, which in the closing position acts, among other effects, on the first conical face and thus causes a resultant force in the axial direction on the valve member. The sealing edge defines the hydraulically effective seat diameter of the valve member and thus, for a given closing force defines the opening pressure of the fuel at which the valve member lifts from the valve seat, counter to the closing force.
The opening pressure of the fuel injection valve depends on the one hand on the closing force acting on the valve member and on the other on the hydraulically effective area of the valve member. In a fuel injection valve, the closing force drops somewhat during operation as a result of relaxation processes in the valve holding body and in the device that generates the closing force. For an optimally functioning fuel injection valve, however, it is important that the opening pressure remain constant during operation. To counteract this relaxation process, the hydraulically effective area of the valve member must decrease. This is achieved by providing that the difference in the cone angles of the valve seat and the first conical face is less than the difference in the cone angles of the second conical face and the valve seat. In operation of the fuel injection valve, the sealing edge presses into the valve seat as a result of plastic deformation, and the hydraulically effective sealing edge shifts from the original sealing edge toward the valve member shaft. This increases the hydraulically effective seat diameter, and the attendant decrease in the area acting in the opening direction compensates at least partly for the dropping closing force, so that the opening pressure remains substantially constant. At a constant closing force, the opening pressure increases accordingly.
In the known valve members, however, it is not possible to determine beforehand how much the hydraulically effective seat diameter of the valve member will change during operation, and thus how markedly the area acting in the opening direction will increase. To achieve at least somewhat replicable results, it is accordingly necessary that both the conical faces and the valve seat be manufactured very exactly and thus cost-intensively.
In an advantageous feature of the subject of the invention, longitudinal grooves are disposed on the conical face between the valve member shaft and the annular groove. This counteracts a cavitation effect in the annular groove with the attendant problems of wear. If the valve member lifts from the valve seat very rapidly, then it can be happen that at the onset of the opening stroke motion, the fuel cannot flow fast enough into the annular groove through the gap formed between the valve member tip and the valve seat. As a result of the longitudinal grooves, the fuel flow from the pressure chamber into the annular groove is improved, and cavitation cannot occur, or can occur only to a markedly reduced extent.